What browser? Does the same thing happen if you try a different browser?
I am able to view images sent in an eBay message in Firefox on a Windows desktop. Unfortunately I do not have an iOS device handy to test.
I know someone might say try the app but then it usually just directs me back to my inbox on the browser.
If you tap and hold down the link it should give you options to use either the app or the browser to open qualified links, and your choice should be remembered the next time you use a similar link.
